[justinsaccount]

The 2nd argument is the 'msg' argument.

With modern features in python you could change the signature to

  assertTrue(expr, *, msg=None)

which would prevent that issue.

[d0mine]

or just:

    assert expr, "custom message"

though given the verbose api, it is ok to require the explicit msg kwarg (duplication in the tests is ok if it makes them more robust)